The vast majority of the volume of the river is diverted into the hydroelectric system for the majority of the year. Yes the river is low, but the falls look like OP's picture very regularly. PSE is required to allow an minimum volume of water pass over the falls regardless of how low the river is, it only looks like your picture when the volume in the river exceeds the capacity of the power stations (which generally occurs on and off for about 7 months out of the year).

Even before the power plants were built, it looked a lot closer to OP's picture than yours during the dry season.